Fluid handling devices (an example of which is described herein as a base unit) can be configured to receive fluid pumping cassettes to actuate membrane-based pumps and valves on the cassette, with a goal of delivering fluid from various sources to various destinations. An advantage of such a system is that the cassette can be discarded after a single use, obviating the need for sterilization and packaging for reuse, and the fluid handling device can remain free from contact with the fluids being processed. Such a system can be used in any application in which fluid pumping is needed and in which disposable fluid-carrying components (such as pump cassettes) are desirable. This is particularly useful in the medical field, because cleaning and sterilization procedures for repeated use of certain fluid-exposed equipment can be expensive, unreliable, and may result in a reduced lifespan of the equipment. Disposable membrane-based pumping cassettes can be used in many medical applications, including, for example, IV infusion devices, extracorporeal blood handling devices, hemodialysis/hemoperfusion devices, body cavity irrigation devices, and automated peritoneal dialysis devices. This technology can similarly be applied to non-medical fluid handling systems in various industries, including biotechnology.
Pumping cassettes may comprise self-enclosed units that include both a fluid flowpath side and an actuation side (commonly pneumatic actuation of membrane-based pumps and valves), the actuation side having one or more attached diaphragms to operate the pumps and valves. The cassettes have ports for connection to fluid sources and destinations. The actuation side of the cassette is configured to be coupled or mated to pressure actuation sources (potentially hydraulic, but more typically pneumatic). Pumping cassettes may also comprise relatively flat, thin housings that include fluid pathways, occludable valve orifices to control the direction of fluid flow in the cassette, and the pumping chamber portion of one or more membrane-based pumps. In one version, these cassettes are typically covered on one or both sides with a flexible membrane fused to the perimeter of the cassette, providing a liquid seal between the fluid paths within the cassette and the outside environment. Both the on-board pumping chambers and valves are operated by having a base unit provide actuation pressure (both positive and negative pressure) to pump actuation regions and valve actuation regions of the outer cassette membrane facing the base unit. This actuation pressure can be delivered by a valved manifold connected to positive and negative pressure sources (e.g. tanks pressurized by separate pumps). The valved manifold can be configured to deliver positive or negative pressure to an installed pump cassette through the use of controller-driven electromechanical valves installed in the manifold. The manifold can deliver the actuation pressure to various valves and pumps of the installed cassette through a pressure delivery block that mates with the cassette, which when mated with adequate force, seals the cassette membrane against various walls defining flowpaths, valves and pumps in the cassette to form sealed fluid flowpaths within the cassette. The pressure delivery block includes pneumatic ports that align with the locations of various valves and pumps on the cassette.
In some embodiments, a gasket can be positioned against the face of the pressure delivery block, the gasket having elastomeric actuation regions that mate with corresponding regions on a cassette membrane when the cassette is installed on the base unit. In this arrangement, the pressure delivery block may also include vacuum ports that penetrate the gasket near the control regions so that a constant vacuum can be applied between the gasket and the membrane of an installed cassette, so that movement of a gasket control region toward or away from the pressure delivery block can be mimicked by the corresponding region of the cassette membrane. The gasket placed over the pressure delivery block can be made of rubber or other elastomeric material, and can provide the method of sealing the cassette membrane against the cassette. The separate pump and valve control regions can be made of the same material, but with varying degrees of thickness or various profiles to deliver positive or negative pressure to the corresponding pump and valve regions of the cassette membrane. The features are designed to form a tight seal between the cassette membrane and the actuation regions of the gasket, so that both outward and inward movement of the control regions of the gasket are followed closely by the adjacent actuation portions of the cassette membrane. Opening and closing of cassette valves, and filling and delivery strokes of the cassette pumps can thus be performed effectively. The control gasket also serves to protect the passageways of the pressure delivery block and the manifold from fluid infiltration should any part of the membrane of an installed cassette fail or become torn or punctured. In medical applications, the interposition of a gasket between the pressure source (air or fluid) and the cassette provides an important safety feature that prevents the actuation fluid or air from being delivered to a cassette (and then possibly to a patient) if the cassette has a punctured or torn membrane.
The way in which the pump and valve control regions of the control gasket are formed and shaped affects the efficiency of fluid pumping by the cassette, and may also affect how accurately the system controller can measure fluid flows in the cassette. The way in which the valve control regions of the control gasket are formed may also affect how much noise or vibration is generated by the pumping system during operation. In the following description, an automated peritoneal dialysis system is used as an example of the implementation these features, but the same principles and solutions can be applied to any fluid handling device—medical or non-medical—that uses membrane-based pump cassettes to move fluid.